We propose to develop a new gene-enzyme system as a probe of eukaryote gene organization. Specifically, we wish to gain an understanding of the regulation of expression of the nervous system enzyme acetylcholinesterase in Drosophila melanogaster. Taking advantage of some of the attractive features of this system, we will study the organization of the acetylcholinesterase structural gene. First, mutant strains will be isolated by: (1) identification of natural variants of acetylcholinesterase, (2) generation of conditional mutants which are sensitive or resistant to anticholinesterase drugs, and (3) production of null-enzyme mutants, which behave as recessive lethals. Mutants which produce structurally defective enzyme molecules will be identified biochemically and immunochemically. These mutants will be subjected to genetic fine structure analysis to delimit the acetylcholinesterase structural sequence. These mutants will also be characterized biochemically, developmentally and behaviorally. In addition, deletion and complementation analysis of the region surrounding the acetylcholinesterase structural gene will be carried out. These experiments will provide the necessary background for screening and characterizing control mutants at this structural gene and elsewhere in the genome, as well as providing the raw material for studying the enzymology of Drosophila acetylcholinesterase.